Local RFS captain Ken Bowerman said the paddocks of a volatile weed, African lovegrass, provided the "perfect fuel" for the fire.

Most residents chose to leave as the fire ominously crept down the hillsides that butt up against rolling farmland.

The fire had until yesterday morning been considered a sidenote to the larger Orroral Valley Fire in Namadgi National Park, which started last week when an Army helicopter landing light set fire to grass.

"They were calling it a spot fire this morning, but it was 1200ha - 1200ha used to be a big fire, I guess that's how bad things are now," one RFS volunteer in Bredbo said.

Flames in the Bega Valley, near Wyndham.

Pyrocumulonimbus clouds form over Candelo. Pictures: Toby Zerna

The village's usual complement of four ageing RFS trucks was bolstered by at least 20 more, with volunteers split into three teams to tackle the dozens of quick-moving grass fires moving ahead of the main firefront.

The fire skipped the border into NSW in the early afternoon, as fire tankers dropped tonnes of pink retardant on the ridge lines and teams of graders cut firebreaks in paddocks between the firefront and the village.

An RFS aerial bomber drops fire repellent near the village of Bredbo. Picture: Gary Ramage

It was expected to jump the Murumbidgee River overnight before burning up steep embankments to the plateaus above the village.

The Clear Range and Orroral Valley fires both triggered emergency warnings yesterday, with the fires expected to merge.

To the north, the Orroral Valley fire could be seen glowing in the hills outside Canberra, where residents of the far southern suburbs were told to remain on high alert in case falling embers sparked fires in the suburbs.

John and Karen McMahon watch from their home as the Big Jack Mountain fire gathers intensity. Picture: Toby Zerna

Down in the Myrtle Mountain, near Bega, many residents chose to stay to fight the mega-blaze that had evolved on the far south coast after the Big Jack Mountain fire joined with the Creewah Rd and Postmans Trail blazes early yesterday.

The combined fires had burnt through more than 20,000 hectares by yesterday afternoon, with water-bombers dumping thousands of megalitres on the blazes to prevent them running through national parks.

Clair Cowie defends her home from a spot fire. Picture: Brook Mitchell/Getty Images

John McMahon, 65, and his wife Karen, 69, who chose to stay to defend their 10ha property said they had too much to lose.

"We have been here since 2004, we have too much to lose. So we are enacting our fire plan and getting ready," Mrs McMahon said.

"We had a big discussion about what we should do this fire season and I am staying with John."